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<p>This study proposes a novel non-contact inspection technique for detecting fatigue cracks in steel structures, specifically targeting the travelling girders of grab-type unloader cranes. These girders are often difficult to inspect due to their height and limited accessibility. The proposed method, called the Active Temperature Gap Method with backside heating, utilizes localized heating on the internal surface of the girder to induce a temperature gap at crack locations, which is then visualized using infrared thermography. Laboratory experiments and finite element (FE) analysis were conducted to determine optimal heating conditions, including heating time and distance. A heat gun was used as a practical heating source, and the effectiveness of both fixed and travelling heating methods was evaluated. The results showed that a heating distance of 30&#xa0;mm and a heating time of 20&#xa0;s provided the best balance between thermal diffusion and crack insulation. Additionally, the use of a travelling heat source significantly improved the uniformity of heating and enhanced crack edge detection. Image processing using the Sobel filter further improved the clarity and accuracy of crack visualization. The method successfully detected both surface and through thickness cracks, even in areas inaccessible from the outside. This approach offers a promising solution for efficient, safe, and cost-effective maintenance of aging industrial infrastructure. Future work will focus on field validation and automation of the heating and image analysis processes to support real time inspection.</p>

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Development of Inspection Method for Steel structure Using Active Temperature Gap Method with Backside Heating

  • 期刊论文

  • 发表日期：

    2026年4月29日

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  • Daisuke Imanishi,
  • Daiki Shiozawa,
  • Takahide Sakagami

摘要

This study proposes a novel non-contact inspection technique for detecting fatigue cracks in steel structures, specifically targeting the travelling girders of grab-type unloader cranes. These girders are often difficult to inspect due to their height and limited accessibility. The proposed method, called the Active Temperature Gap Method with backside heating, utilizes localized heating on the internal surface of the girder to induce a temperature gap at crack locations, which is then visualized using infrared thermography. Laboratory experiments and finite element (FE) analysis were conducted to determine optimal heating conditions, including heating time and distance. A heat gun was used as a practical heating source, and the effectiveness of both fixed and travelling heating methods was evaluated. The results showed that a heating distance of 30 mm and a heating time of 20 s provided the best balance between thermal diffusion and crack insulation. Additionally, the use of a travelling heat source significantly improved the uniformity of heating and enhanced crack edge detection. Image processing using the Sobel filter further improved the clarity and accuracy of crack visualization. The method successfully detected both surface and through thickness cracks, even in areas inaccessible from the outside. This approach offers a promising solution for efficient, safe, and cost-effective maintenance of aging industrial infrastructure. Future work will focus on field validation and automation of the heating and image analysis processes to support real time inspection.